The present invention relates to an interconnection forming method utilizing an inorganic antireflection layer.
Now, a conventional interconnection forming method utilizing an inorganic antireflection layer will be described with reference to FIG. 1, which is a diagrammatic sectional view of a semiconductor device for illustrating a technology of the interconnection forming method utilizing the conventional inorganic antireflection layer.
As shown in FIG. 1, when it is attempted to pattern a metal multi-layer 3 formed on an insulator film 2 formed on a silicon substrate 1, it is necessary to first pattern a photo resist (lithography). Ordinarily, the lithography is carried out by (1) depositing a photo resist on a wafer (on the insulator film 2 in this case) (resist deposition step), (2) exposing the photo resist to a desired pattern (exposure step), (3) developing the exposed resist (development step), and (4) checking whether or not the size of the pattern of the developed resist is satisfactory, whether or not the pattern of the developed resist is broken, and whether or not the pattern of the developed resist is deviated (check step).
Incidentally, in the check step of the lithography, if it is judged that the pattern of the developed resist is defective, it is necessary to execute the lithography again from the resist deposition step. However, since the patterned resist remains on the wafer, it is necessary to remove the remaining resist. For this purpose, the remaining resist is ashed with oxygen plasma or ozone and wet-removed with an organic removing liquid (removing step). Thereafter, the resist deposition step, the exposure step, the development step, and the check step are carried out. A process composed of the removing step, the resist deposition step, the exposure step, the development step, and the check step, is called a xe2x80x9creworkxe2x80x9d.
In a patterning for a micro lithography, in particular, the lithography having a line width of a sub-micro or less, the photo resist is exposed by an excimer laser. However, the photo resist for the excimer laser has a tendency that the photo resist is thinned or disappears by reflection from a concavo-convex surface of the underlying film. In order to prevent this inconvenience, a TiN antireflection film 4 is formed on the metal multi-layer film 3, as shown in FIG. 1.
Recently, furthermore, although not shown in FIG. 1, it has been proposed to form on the TiN antireflection film 4 an organic antireflection coating (a nature near to the photo resist or a silica based type) or an inorganic antireflection layer (SiON film).
Comparing the organic antireflection coating with the inorganic antireflection layer, the inorganic antireflection layer is more excellent than the organic antireflection coating from the view point that a dry etching machines can be used and from the view point of the rework in the lithography.
The reason for this is that in the case of the organic antireflection coating, when the resist is removed, the organic antireflection coating will be removed together with the resist, and therefore, it is necessary to deposit the organic antireflection coating once again. Accordingly, the number of steps in the rework of the lithography becomes much than that required when the inorganic antireflection layer is used, by one.
On the other hand, after the metal multi-layer film under the patterned resist is dry-etched using the patterned resist as a mask, the resist and others are removed, use of the inorganic antireflection layer needs one or two additional steps in comparison with use of the organic antireflection coating.
Furthermore, in connection with an etching chamber, an etching gas for the organic antireflection coating inevitably etches a deposition adhered in the etching chamber, with the result that an increase of so called particles and a problem of flaking are apt to occur.
At the present time, when the organic antireflection coating is formed on an AlCu film constituting a metal interconnection (precisely, on TiN film formed on the AlCu film), the rework becomes difficult, because both of the organic antireflection coating and the resist for the Kr laser are difficult to remove, so that a residue remains.
In addition, the particles generated in the etching step are a significant problem. The organic antireflection coating is not suitable when the AlCu film is etched. However, the organic antireflection coating is used on a polysilicon film and a silicide film.
Because of the above mentioned reasons, when the antireflection coating is used in the lithography for preparation of the patterning of the metal interconnection, it is preferred to use the inorganic antireflection layer.
However, a problem has been encountered when the inorganic antireflection layer is used as the antireflection coating.
Japanese Patent Application Pre-examination Publication No. JP-A-09-055351 (an English abstract of which is available from the Japanese Patent Office Home Page and the content of the English abstract is also incorporated by reference in its entirety into this application) proposes a method including the steps of depositing an antireflection coating formed of a SiON film on an interconnection layer, and executing a plasma treatment by N2, O2 and others to convert the nature of the surface of the SiON film so as to form a protection film, for the purpose of stabilizing the surface of the antireflection coating. In the structure formed by this method, however, the nature is converted in only the thickness of a few 10 xc3x85 at the surface of the SiON film. Therefore, if it is kept as it is, the surface is stable, but it is sensitive to a chemical treatment such as the rework of the lithography, so that the film nature is changed with high possibility.
Accordingly, it is an object of the present invention to provide an interconnection forming method utilizing an inorganic antireflection layer, which has overcome the above mentioned problems.
Another object of the present invention is to provide an interconnection forming method utilizing an inorganic antireflection layer, which is hard of changing its film nature even if it is subjected to a wet removing treatment and a plasma ashing for the resist when the rework of the lithography becomes necessary because of a misalignment of the patterned resist (to such a degree that the patterned resist is deviated from the underlying pattern to make a circuit formation impossible) and/or another patterning defective in the lithography.
The above and other objects of the present invention are achieved in accordance with the present invention by an interconnection forming method utilizing an inorganic antireflection layer, wherein an inorganic antireflection layer is formed by forming an inorganic metal type antireflection film on a metal interconnection layer, depositing a plasma SiON film on the inorganic metal type antireflection film, and depositing a plasma SiO2 film on the plasma SiON film. Here, the inorganic metal type antireflection film can be formed of for example a TiN film, but is in no way limited to only the TiN film.
In one embodiment of the interconnection forming method utilizing the inorganic antireflection layer in accordance with the present invention, the inorganic antireflection layer is continuously dry-etched by use of a gas including Cl2, in a chamber in which the metal interconnection layer is dry-etched, so that the inorganic antireflection layer and the metal interconnection layer are continuously dry-etched in the same chamber. Furthermore, in this continuous dry-etching, the inorganic antireflection layer is dry-etched under a condition having a high ratio of BCl3, and the metal interconnection layer is dry-etched under a condition having a low ratio of BCl3.
In a preferred embodiment of the interconnection forming method utilizing the inorganic antireflection layer in accordance with the present invention, after the above mentioned continuous dry-etching, an over-etching process is carried out by a dry etching, and furthermore, after an ashing treatment is carried out, a wet removing treatment is carried out by using an organic removing liquid including 0.1% to 3% of ammonium fluoride and 10% to 80% of water, so that an etching deposition which occurred in the dry etching is removed together with the inorganic antireflection layer.
If the removing effect by the organic removing liquid is not satisfactory, in order to make it easy to remove the inorganic antireflection layer, an oxide film dry etching and an ashing using an O2/CF4gas containing CF4 of 0% to 10% in the ratio to the amount of O2, are carried out before the removing treatment by the organic removing liquid.
If the plasma SiON of the inorganic antireflection layer remains, after an interlayer insulator film is formed, a via hole is formed by a via hole etching, and then, the remaining plasma SiON at the bottom of the via hole is removed by an organic removing liquid.
In another preferred embodiment, a hard mask formed of an insulator film such as a plasma SiON film, is formed between the plasma SiON film and the inorganic metal type antireflection film of the inorganic antireflection layer.
In this case, after the plasma SiON film of the inorganic antireflection layer and the hard mask are dry-etched, the resist is removed by the ashing, and thereafter, the metal interconnection layer is dry-etched by using the hard mask.
Alternatively, just before the dry etching of the metal interconnection layer, the wet removing treatment using the organic removing liquid is carried out, so that the plasma SiON film of the inorganic antireflection layer and the deposition are removed, and thereafter, the metal interconnection layer is dry-etched.
As mentioned above, in the interconnection forming method utilizing the inorganic antireflection layer in accordance with the present invention, two kinds of antireflection layer, namely, the inorganic metal type antireflection film and an ARL-SiON film (plasma SiO2 film+plasma SiON film) are deposited on the metal interconnection layer (a metal multi-layer film composed of a combination of any at least two of AlCu, TiN, TiW and Ti). With this feature, it is possible to minimize a halation attributable to a concavo-convex surface of the metal interconnection layer.
Furthermore, the resistance to migration is not lowered, and the resistance of a via hole contact connecting between interconnections of different levels does not increase. In this connection, not only the film thickness and the film quality of the ARL-SiON film is optimized to minimize the reflectance factor of the metal interconnection layer, but also the composition of the ARL-SiON film is so adjusted that the ARL-SiON film can be easily dissolved by a hydrofluoric acid in a later process.
In the case that the inorganic antireflection layer composed of the inorganic metal type antireflection film and the ARL-SiON film, and the underlying metal interconnection layer are continuously dry-etched in the same processing chamber, the basis of the etching gas is composed of a combination of chlorine based gases (Cl containing gas such as Cl2, BCl3, HCl) which is the same as that used for etching the metal film. Therefore, the change of the atmosphere within the processing chamber can be limited to a minimum.
Furthermore, in the case that the etching gas composed of a combination of Cl2 and BCl3 is used, it is possible to adjust the CD (critical dimension) shift amount and the selective etching ratio between the inorganic antireflection layer and the photo resist, by changing the mixing ratio of the etching gas. Here, assuming that the resist pattern size in the lithography is expressed by xe2x80x9cCD1xe2x80x9d and the resist pattern size after the etching is expressed by xe2x80x9cCD2xe2x80x9d, the CD shift amount can be defined as the difference xe2x80x9cCD1xe2x88x92CD2xe2x80x9d.
As mentioned above, it is possible to overcome the problems in the lithography by forming on the metal interconnection layer the inorganic antireflection layer composed of the inorganic metal type antireflection film and the ARL-SiON film. However, if the SiON remains on the metal interconnection film, it is expected that an inconvenience occurs. This inconvenience can be exemplified by a stopping of an etching in a via hole forming processing or a lowered reliability of the interlayer insulator film or a film peeling-off. However, the ARL-SiON film can be effectively removed by the organic removing liquid including the ammonium fluoride and the water.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.